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UM10237 NXP Semiconductors Chapter 2: LPC2468 memory map 4. LPC2400 memory re-mapping and boot ROM 4.1 Memory map concepts and operating modes The basic concept on the LPC2400 is that each memory area has a "natural" location in the memory map. This is the address range for which code residing in that area is written. The bulk of each memory space remains permanently fixed in the same location, eliminating the need to have portions of the code designed to run in different address ranges. Because of the location of the interrupt vectors on the ARM7 processor (at addresses 0x0000 0000 through 0x0000 001C, as shown in Table 2–5 below), a small portion of the Boot ROM and SRAM spaces need to be re-mapped in order to allow alternative uses of interrupts in the different operating modes described in Table 2–6. Re-mapping of the interrupts is accomplished via the Memory Mapping Control feature (Section 2–5 “Memory mapping control” on page 15). Table 5. ARM exception vector locations Address Exception 0x0000 0000 Reset 0x0000 0004 Undefined Instruction 0x0000 0008 Software Interrupt 0x0000 000C Prefetch Abort (instruction fetch memory fault) 0x0000 0010 Data Abort (data access memory fault) 0x0000 0014 Reserved Note: Identified as reserved in ARM documentation, this location is used by the Boot Loader as the Valid User Program key. This is described in detail in "Flash Memory System and Programming" chapter on page 561. 0x0000 0018 IRQ 0x0000 001C FIQ Table 6. LPC2400 Memory mapping modes Mode Activation Usage Boot Loader mode Hardware activation by any Reset The Boot Loader always executes after any reset. The Boot ROM interrupt vectors are mapped to the bottom of memory to allow handling exceptions and using interrupts during the Boot Loading process. A sector of the flash memory (the Boot flash) is available to hold part of the Boot Code. User Flash mode Software activation by Boot code Activated by the Boot Loader when a valid User Program Signature is recognized in memory and Boot Loader operation is not forced. Interrupt vectors are not re-mapped and are found in the bottom of the flash memory. User RAM Software Activated by a User Program as desired. Interrupt vectors are mode activation by re-mapped to the bottom of the Static RAM. User program UM10237_1 User manual © NXP B.V. 2006. All rights reserved. Rev. 01 — 18 December 2006 14 of 664
